Montmorillonite polymer concrete: Zero‐shrinkage and expanding polymer concrete with enhanced strength

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Abstract
Conventional polymer concrete (PC) suffers from setting stresses, generated during the cure of the resin binder, when polymerization shrinkage is hindered by the close packing of filler and aggregate particles. Setting stresses impair significantly the strength of the cured PC. Current zero‐shrinkage and expanding PC formulations achieve these properties with a sacrifice in strength. Here we present a novel method for producing zero‐shrinkage and expanding PC systems with concomitant enhancement in strength. This is achieved by dispersing small amounts of the mineral montmorillonite (MMT) into the resin. As the system cures, the resin interacts with the hydrated mineral: at temperatures above 100°C some of the hydration water is released, creating expansion forces, which counteract resin shrinkage. MMT contents of 0.2 percent or less give rise to zero‐shrinkage polyester PC systems with flexural strength 30 percent greater than the corresponding conventional PC; higher MMT contents create PC systems that expand upon curing or generate hydrostatic pressure during constant‐volume cure. We discuss the effects of MMT content and cure temperature on the volume change and strength of the resulting PC. We then propose a mechanism for the action of MMT as a highstrength expansion agent, based on differential scanning calorimetry and thermomechanical analysis of these systems.